calculating displacement with solidworks

Discussion in 'Boat Design' started by deck work shop, Dec 6, 2015.

  1. deck work shop
    Joined: Nov 2015
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    deck work shop Junior Member

    there are some easy and useful methods for calculating displacement and water line by solid works .
     

    Attached Files:

  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    The only thing, I think, can be commented, with the models shown by you, it is that you should change the coordinate system so that the extracted data to be useful in naval architecture calculations.
     
  3. John Perry
    Joined: Nov 2003
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    John Perry Senior Member

    I am slightly puzzled by the screenshot that the OP provides since this suggests that you would use the measure tool in SolidWorks to find the displacement of a hull - surely you would just use the mass properties tool. Once you have the immersed part of the hull as a solid body with the material set to water, or sea water, one click on the 'mass properties' button tells you all you could want to know about displacement, centre of buoyancy etc. I don't have the naval architecture plugin(s) for SolidWorks, but presumably this would automate the process making it even easier.

    While I am here, this is roughly the sequence of work I have followed when I have drawn boats with SolidWorks.

    1. Produce a part file that contains no solids or surfaces at all - it is just a collection of related 'unabsorbed sketches'. These sketches show the boat in elevation and plan and define all the basic dimensions that govern hull shape and the location of bulkheads and the main items of equipment rig etc.

    2. I make a lot of use of the ability of SW to insert one part into another. So the next step would be to take the part from 1. above and insert it into a new part that is then developed into a solid model of the hull with no detail other than the basic external form.

    3. Insert the part produced in 2 into a new part that will be used for hydrostatic calculation. This part chops off the hullshape above the waterline, sets the material to water and calculates displacement (only a preliminary estimate at this stage)

    4 If it is a chined hull, insert the part produced in 2 into a new part that will be used for modelling the skin panels of the hull and developing these as flattened forms the shape of which can be exported as dxf files for cnc cutting.

    5. Insert the parts produced in both 1 and 2 into a new part that will become a detailed model of the hull. If it is a multihull design I would probably repeat this for each hull then for the connecting structure. At this stage I make a lot of use of the ability of SW to produce parts with mulitple bodies. The model I made for an individual hull of a ply/epoxy catamaran a few years back was a single 'part' but would have hundreds, maybe thousands of individual solid bodies since it was detailed down to every separate piece of timber, every door hinge, galley equipment etc. However, items that move relative to the fixed structure are all modeled as separate parts rather than bodies in a multibody part, so as to allow moving parts to be animated to check working clearances etc. Hence rudders, parts for the steering linkage, hinged/sliding hatches, windows and doors, winch handles etc. all modelled as separate part files. Items that have weight but for which geometry is not important or not known are modelled as small cylinders, correctly located and of a very heavy material (much heavier than any real material). So, for example, a person would be modelled as a tiny cylinder that would hardly be visible in the final views, the cabin baggage associated with that person would be similarly modelled and appropriately located within the boat.

    6. Assemble everything together as an assembly file. If everything is included in the model and the materials all set correctly, a single click on 'mass properties' gives weight and cog. Then go back to the part produced in 3. and adjust the waterline - an iterative process that quite quickly finds the correct waterline to a reasonable degree of accuracy. Of course, for a monohull sailing boat you may want to repeat this for several angles of heel, which will be a bit more tedious but still quite feasible.

    The advantage of step 1 above is that you have a set of sketches all in one file that you can edit to change any of the basic dimensions so that everything else updates to suit - in theory anyway.

    I am sure this is not the only way to go about the task, just the way I have found works for me.
     
  4. deck work shop
    Joined: Nov 2015
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    deck work shop Junior Member

    when u have a solid part as a boat body you can simply calculate the displacement .
    1.close the top of boat with a thin extrude .
    2.extrude a non merged part (box) surrounding your part .
    3.use combine command and subtract two bodies.
    4.you will have the option to choose which part you want and you have to choose the part which represent the inside volume of the boat.
    5.save this file
    6.open a new assembly file .import your boat and inside volume in and place inside volume in it position . now set the material to water .
    7.make a cut extrude and start too cut the part from top check the mass property . do this procedure until your mass become equal to the mass of your boat.
     

  5. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Everything you explain the procedure is very obvious. It can be done with any CAD program. The problem is how to do it not to waste too much time on it.
    This can obtain two values (draft and displacement) of the more than 15 values that are included in a regular study of hydrostatic values. How to get the other hydrostatic values?
    With all due respect for your work but, is it worth trying to figure out how to get them (with solidworks)?
     
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